A precision pointing system carrying a sensor, such as a telescope as its payload, may be susceptible to disturbances that produce structural vibrations and, consequently, pointing errors. Such vibrations may be attributed to mechanical components or assemblies, such as reaction wheel assemblies that are used as actuators in the precision pointing system. For the most part, because these systems tend not to have significant, inherent damping, these structural vibrations may degrade system performance and even cause structural fatigue over time. Therefore, an efficient means of providing damping and isolation to the system may be needed.
Typically, to minimize performance degradation caused by vibrations, a passive-mass damping and isolation system is used for damping the structure and isolating the payload carried by a precision isolation system. One example of a passive-mass damping and isolation system is the D-STRUT® isolation strut, manufactured by Honeywell, Inc. of Morristown, N.J. The D-STRUT® isolation strut is a three-parameter vibration isolation system that mechanically acts like a spring (KA) in parallel with a series spring (KB) and damper (CA) and is disclosed in U.S. Pat. No. 5,332,070 entitled “Three Parameter Viscous Damper and Isolator” by Davis et al. This patent is hereby incorporated by reference.
The D-STRUT® isolation strut includes a hollow shaft and a piston that is configured to slidably move through the shaft. The piston includes a flange that extends radially from a midsection thereof. The flange has a top surface that is coupled to a first sealed bellows and a bottom surface that is coupled to a second sealed bellows. Each of the bellows has a chamber that is filled with fluid. Thus, when the piston moves axially through the shaft, fluid flows from one of the bellows chambers to the other.
Although the D-STRUT® isolation strut operates effectively in most applications, it may not be appropriate to implement in other applications. For example, in circumstances in which a space constraint includes the need for an elongated isolation strut, lengthening the first and second sealed bellows to accommodate such a space constraint may present certain drawbacks. In particular, if one of the first and/or second sealed bellows is too long, it may experience column buckling when force is applied to the piston. As a result, the amount of force applied to the piston may need to be decreased to avoid column buckling of either the first and/or second sealed bellows; thus, the isolation strut may not be able to damp vibration of relatively large payloads. In another example, an apparatus may already implement the D-STRUT® isolation strut; however, there may be a desire to replace the strut with one that has an increased payload capacity. In such cases, complicated and more costly configurations are typically employed.
Accordingly, it is desirable to have an isolation strut that is capable of damping and isolating vibration of relatively large payloads without experiencing column buckling either the first and/or second sealed bellows. In addition, it is desirable for the isolation strut to be usable in any type of space constraint. Moreover, it is desirable for the isolation strut to have a simple configuration that is relatively inexpensive to implement. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.